Not Mine by OhMyNanase
Makoto would do absolutely anything for Haru. He loves him with all his heart, mind and soul, and wishes he could express his feelings to him. However, there's an obstacle in the way; Haru has been in a relationship with Rin for years, but there is trouble in paradise. Every time Rin and Haru have an argument, Haru seeks solace and comfort in Makoto. He wishes things could be different and that he didn't hurt each time Haru returned to Rin, but he could never turn his back on the man he loves.
Wow! This story is so beautiful! Your heart will break for Makoto, Haru and Rin as you witness their trials and tribulations, but the story isn't all angst. There are some really cute and humorous moments as well. Give this story a try!
artwork credit: strawberry4750